Kinetics of ultrasonic degradation and polymerisation degree distribution of sonochemically degraded chitosans

The process of physical degradation by means of the ultrasonic action towards chitosans with mole fraction of 2-acetamido-2-deoxy-β- -glucopyranose units (the degree of N-acetylation, F_A) in the range of 0.10≤F_A≤0.28, and the weight average polymerisation degree in the range of has been investigated. The decrease of as well as changes in the distribution of the degree of polymerisation (P) has been determined as a function of time, F_A, temperature, concentration of chitosan solution and concentration of acetic acid in the solution. The use of low-power ultrasound emitter allowed to establish that in the case of chitosan (binary heteropolysaccharide) the general rate parameter (k) increased with F_A. This can be explained by the relatively stronger aggregation of macromolecules with higher F_A, which results in size increase of macromolecular individuals and hence in their higher susceptibility to ultrasonic action. It was also observed that k decreased with chitosan concentration and temperature. The value of limiting degree of polimerisation (x_e) was found to be influenced by structural parameters of chitosan chains (F_A, aggregation). The increase of acetic acid concentration caused the increase in the k value, what indicated accelerating effect of ultrasound towards acidic hydrolysis of chitosan. The shape of the P curve of sonochemically degraded chitosans are in good correlation with the mid-point breakage concept of degradation accepted in sonochemical degradation of polymers.     

Genotoxicity of alpha-asarone analogues

The role of cholesterol in the formation of atherosclerotic lesions during hypercholesterolemia has been confirmed. alpha-Asarone is a substance of a potent hypolipidemic activity which is isolated from plants. We previously described the synthesis of several alpha-asarone analogues exhibiting hypolipidemic and antiplatelet activity. Genotoxic activity of four selected alpha-asarone analogues was theoretically evaluated based on quantum-mechanical method for calculation of enthalpy of carbocations formation (DeltaH(R)) according to the Testa's method. In the present paper, we evaluated the mutagenic and genotoxic activity of alpha-asarone isomers 2-5 based on the reference Ames test and micronucleus test. Results obtained in the study show that tested isomers were non-mutagenic, however, they exhibited growing cytotoxic activity. Relationship between the heat of formation of their putative metabolic intermediates and mutagenic/genotoxic activity was not confirmed.     

Design and synthesis of new substrates of HtrA2 protease

HtrA2 belongs to the HtrA (high temperature requirement A) family of ATP-independent serine proteases. The primary function of HtrA2 includes maintaining the mitochondria homeostasis, cell death (by apoptosis, necrosis, or anoikis), and contribution to the cell signaling. Several recent reports have shown involvement of HtrA2 in development of cancer and neurodegenerative disorders. Here, we describe the profiling of HtrA2 protease substrate specificity via the combinatorial chemistry approach that led to the selection of novel intramolecularly quenched substrates. For all synthesized compounds, the highest HtrA2-mediated hydrolysis efficiency and selectivity among tested HtrA family members was observed for ABZ-Ile-Met-Thr-Abu-Tyr-Met-Phe-Tyr(3-NO₂)-NH₂, which displayed a specificity constant k_cat/K_M value of 14,535 M⁻¹ s⁻¹.     

Effects of Top‐Soil Preparation and Broad‐Leaved Tree Mixture on Carabid Beetles in Afforested Fallow Plots

A 2‐year study to evaluate the effect of four soil preparation techniques and four species compositions in a pine plantation with an admixture of broad‐leaved trees on the species diversity and structure of ground beetle assemblages (Carabidae) was conducted. The soil preparation techniques were full shallow agricultural plowing (25 cm deep with three variants—plowing, plowing with ridge formation, and plowing with subsoiling) and full deep plowing (50 cm deep). The plantation species compositions were pine 7000/hectare, pine 5500/hectare + broad‐leaved species 1500/hectare, pine 4000/hectare + broad‐leaved species 3000/hectare, and pine 2000/hectare + broad‐leaved species 5000/hectare. Carabidae were sampled monthly with pitfall traps in the plantation from May to November in 2003 and 2004—the fourth and fifth years after afforestation. Only the soil preparation technique affected species diversity. The mean number of carabid species and the Shannon–Wiener index were higher in the case of the full agriculture plowing with subsoiling treatment and the full agriculture plowing with ridge formation than in the full shallow agriculture plowing. The structure of the assemblages was dependent on the soil preparation technique, but not on tree species composition. In general, deep plowing and shallow plowing with subsoiling were conducive to an increase in the proportion of individuals representing late succession species, whereas shallow plowing favored early succession species. The results suggest that for effective plantation of a managed stand, deep plowing or shallow plowing with subsoiling is more beneficial for afforestation of fallow fields than typical shallow agricultural plowing.     

Interspecific differences in root architecture among maize and triticale genotypes grown under drought,waterlogging and soil compaction

Environmental stresses (soil compaction, drought, waterlogging) cause changes in plants’ root system structure, also affecting the growth of above-ground parts. The aim of this study was to estimate phenotypic variation among maize and triticale genotypes in root penetration ability through petrolatum-wax-layer (RPA). Also, the effect of shortage or excess of soil water on dry matter of shoots and roots and morphological changes in root system structure in sensitive and resistant maize and triticale genotypes grown in low or high soil compaction level was evaluated. To estimate RPA index, the petrolatum-wax-layer method (PWL) was used. The strength of three petrolatum-wax concentrations 60, 50 and 40 % was 0.52, 1.07 and 1.58 MPa, respectively. High coefficients of variation (CV) were observed in 0.52 and 1.07 MPa and for maize were 19.2 and 21.7 %, and for triticale, 12.5 and 18.3 %, respectively. The data indicate that the use of PWL technique is an effective screening method, and makes it possible to divide the genotypes into resistant and sensitive groups. The second part of this study investigated a multistress effect of soil compaction combined with drought or waterlogging on root and shoot growth and morphological changes in root system structure of maize and triticale genotypes differing in susceptibility to environmental stresses. Seedlings were grown for 4 weeks in root-boxes under conditions of low (LSC 1.1 g cm^?3) or severe (SSC 1.6 g cm^?3) soil compaction. Drought or waterlogging stresses were applied for 2 weeks from 14th to 28th day. In comparison to LSC treatment, in SSC treatment the decrease in dry matter of shoots and roots was greater for sensitive genotypes of maize and triticale (Ancora, CHD-147). Soil drought or waterlogging caused greater decrease of dry matter of shoots and roots in seedlings grown in SSC in comparison to LSC. The root penetration index (RPI) was estimated as a ratio of root dry matter in 15–40 cm root-box layer to total root dry matter. On the basis of RPI it was possible to group the genotypes according to their ability to distribute roots in soil profile. In comparison to LSC, SSC exerted a strong influence on the length of seminal and seminal adventitious roots, as well as the number and length of L- and S-type lateral roots developed on seminal and nodal roots. In both species the restriction effect of soil compaction on number and length of roots was more severe in sensitive (Ankora, CHD-147) than in resistant (Tina, CHD-247) genotypes. The restriction in roots propagation was greater in triticale than in maize. Exposure to drought or waterlogging in the case of genotypes grown in LSC and SSC treatments caused a decrease in number and length of particular components of root system structure. In both species the decrease of root number and length in plants grown under waterlogging was greater than under drought. The observed changes in root system were greater in sensitive (Ankora, CHD147) than in resistant (Tina, CHD-247) genotypes. Statistically significant correlations were found between RPA and RPI and also between these indexes and soil compaction, drought and waterlogging susceptibility indexes. This indicates that genotypes resistant to soil compaction were resistant to drought or waterlogging and also that genotypes resistant to drought were resistant to waterlogging.     

Predator-induced diapause in Daphnia magna may require two chemical cues

The production of diapausing eggs by Daphnia magna stimulated by fish exudates can be explained as an anti-predator defence ensuring genome protection in periods of high risk from fish predation. The combined effects on the induction of D. magna diapause of an “alarm” chemical originating from injured conspecific prey and fish kairomones were tested. The results of the experiment showed that the cues when present together promote both the production of ephippial eggs and male formation, indicating their role in the synchronization of the entire mode of Daphnia sexual reproduction. Ephippial eggs were only produced in the presence of both fish kairomone and conspecific alarm chemicals, while male offspring occurred in the treatments where both, one or none of the cues were present. However, production of males was the highest when both cues were provided. D. magna responded similarly to the tested cues whether or not the hypothetical alarm substance associated with predator odour came from Daphnia specimens actually eaten by fish or from crushed conspecific individuals. However, chemicals from crushed chironomid larvae combined with fish kairomones did not induce a similar response in D. magna. The relative advantage of utilization of alarm cues or predator kairomones in the induction of defence responses in prey organisms is discussed. Received: 8 June 1998 / Accepted: 11 January 1999